The present invention relates to a power semiconductor module that incorporates a plurality of semiconductor elements constituting a bridge circuit, such as an insulating gate bipolar transistor (hereafter referred to as an "IGBT"), a bipolar transistor, or a MOS transistor, together with related circuits. The module is used to drive a load, such as an electric motor.
The power semiconductor elements, such as IGBTS, described above, which are used to drive various loads, such as electric motors, are generally incorporated in devices as individual elements housed in a package. In 2- or 3-phase bridge circuit devices using four to six power semiconductor elements, however, these semiconductor elements can be mounted as chips on a heat sink or an insulating substrate thermally closely coupled thereto, which is then housed in a case. This module is advantageous due to its reduced overall size and thermal radiation. Furthermore, the recent tendency is to incorporate into this module an integrated circuit chip comprising a combination of the power semiconductor elements and related circuits, such as drive circuits for the elements. This invention relates to a semiconductor module incorporating a plurality of power semiconductor elements together with related circuits as described above, and FIG. 2 shows a typical conventional example.
The module 70 shown in FIG. 2 comprises a 3-phase bridge circuit including six IGBTs 10 and related circuits, both of which are incorporated in a case 60. The module 70 is a small power inverter that receives at its positive and negative input terminals P and N a DC voltage from a power supply 1 (on the left of this figure) to drive a load 2, such as an electric motor, connected to three output terminals U, V, and W (on the right of this figure), in response to instructions from a controller 3 (at the bottom of this figure) that is a microcomputer.
Each of the IGBTs forming the three semiconductor elements 10 on each of the upper and lower arms of the bridge circuit includes an auxiliary emitter 10a for detecting a current and has a free wheeling diode 11 connected in reverse parallel therewith so as to allow the module to function as an inverter. These semiconductor elements 10 and diodes 11 are mounted as chips on a heat sink or a ceramic substrate thermally closely coupled thereto, which are then housed in a plastic frame-like case 60 together with wiring conductors 40 required to connect these elements together or with terminals. An epoxy resin is then poured into the case to integrate the elements into a module 70 having a robust structure. For the purposes of illustration, the input and output terminals are shown to protrude laterally from the case 60, but in fact, they are generally drawn out from the top surface of the case 60.
A circuit for controlling the plurality of power semiconductor elements is integrated as a single chip and incorporated in the case 60 of the module 70 as a controller 80. The controller 80, which includes drive protection circuits 81 and 82 corresponding to the semiconductor elements 10 on the upper and lower arms, is connected to the controller 3 via a bus 3a and a group of terminals Tc, and receives from the controller 3 three control signals (u), (v) and (w) for the output terminals U, V and W for three phases to issue a corresponding drive instruction Sd from the drive protection circuits 81 and 82 to the corresponding semiconductor elements 10. When a defect occurs, the controller 80 receives an electric signal Si from the auxiliary emitter 10a of the semiconductor elements 10 at the drive protection circuits 81 and 82 to stop the drive instruction Sd in order to protect the semiconductor elements 10 while sending a warning signal Sa to the controller 3.
The controller 80 can be operated by applying a low power voltage Ed thereto, and the ground potential Ee can be set at the same potential as the negative input terminal N of the power bridge circuit as shown in the figure. Since, however, the drive protection circuits 81 and 82 must be operated at the same potential as the corresponding semiconductor elements 10, the emitter potentials of the semiconductor elements 10 are provided to these circuits via a potential transmission lines 42. Since the three semiconductor elements on the upper arm operate at different emitter potentials, power voltages Eu, Ev and Ew are provided to the corresponding drive protection circuits 81, respectively, via feeding lines 41. On the other hand, the three semiconductor elements 10 on the lower arm are operated at the same emitter potentials, so a power voltage Ec is commonly provided to the corresponding drive protection circuits 82 via a feeding line 41'. The reference potential for the power voltages Eu, Ev and Ew must be a higher voltage similar to that in the positive input terminal P of the bridge circuit.
Although the size and cost of the conventional module 70 described above are significantly improved as compared to a structure with individual elements, this module has also cost and performance problems as the range of its application increases. The largest problem in cost is the difficulty in reducing the size of the controller chip 80, to thereby cause high cost. This is because a large chip area is required to join and separate the controller body and the drive protection circuits 81 and 82, especially the circuits 81, which operate at different potentials as described above when these components are incorporated into the controller 80. In other words, the area required for such pn junction isolation can not be reduced no matter how highly these circuits are integrated. Accordingly, the chip size cannot be reduced below a certain limit, and this prevents the cost from being reduced sufficiently.
The second problem in cost is the large number of lines including the signal lines 50 between the plurality of semiconductor elements 10 constituting the bridge circuit and the controller 80, and the feeding lines 41 and potential transmission lines 42 to the controller 80, as well as the large amount of labor required to connect these lines. In particular, the improvement of the protection level for the semiconductor elements 10 has recently been requested. Also, in order to provide not only overcurrent protection but also short-circuit and overheat protections, the number of signal lines 50 must be increased correspondingly, resulting in increase of the amount of labor. In addition, in order to prevent the internal connection lines from becoming complicated, the size of the case 60 and thus the module 70 must be increased.
A performance problem is that malfunction caused by entering or invading of noise into the signal lines 50 or the interference of signals with each other happens easily. That is, since the signal lines 50 must be as short as possible due to the structure of the module 70, the lines 50 unavoidably pick up noise. In addition, the drive instruction Sd and the current signal Si are both sharp pulse-like signals and the lines 50 are likely to be complicated or mixed if there are a large number of signal lines 50, so that interference is likely to happen with each other. To avoid noise and signal interference, electrostatic shielding can be effectively applied to the signal lines 50 and the controller chip 80. In this case, however, it must have a disadvantage in size and cost.
In view of the above problems, it is an object of the invention to keep the most of the above advantages that the semiconductor module for the power bridge circuit has and to improve the module in terms of cost and performance.